Scientists have discovered a new marker for depression that could pave the way to a blood test for the notoriously hard-to-diagnose disorder.
Depression strikes more than 16 million Americans, making it the leading cause of disability in the country.
Many more people likely suffer from the disorder but go undiagnosed. Even if they had access to care, there are no clear-cut diagnostic methods to test for depression to guarantee that those in need of help are identified.
Subjective assessments, while well-intentioned, cannot parse out the finer types of depression or provide a perfect measure of the severity of a person’s depression.
But now scientists at Rockefeller University have found that those with depression have lower levels of a key molecule in their blood, an unprecedented indicator of mental illness that could open the door for the development of a blood test.
Millions of Americans suffer from depression, and many more people likely go undiagnosed, but the discovery of a biomarker for the mental illness could pave the way to a blood test
Organizations of medical professionals across many specialties – from general practitioners to pediatricians and gynecologists and obstetricians – have been urging their colleagues to screen more patients more thoroughly for depression.
Incorporating screenings into standard medical care is a good place to start, but diagnoses are only as accurate as the tool used to make them.
Depression screenings typically consist of a series of questions in written or verbal form asked by a doctor to a patient and perhaps their loved ones.
If depression is a symptoms of another problem – such as a thyroid condition – blood tests for the underlying problem could also confirm (or deny) that a person has related depression, but not if they had the mood disorder independently.
More likely, a doctor would just use the blood test to rule out underlying causes of depression.
The rest of a diagnosis is very much up to the judgement of a doctor. The result is that many people in need of therapy, medication or both, slip through the cracks and continue to suffer.
In what was widely regarded as a misguided attempt to fill in some of that diagnostic gap, Google introduced its own online depression test, PHQ-9, last year.
While it gave great access to a screening tool, some experts saw it as dangerously reductive, while others voiced concern over data privacy.
Better, more precise medical diagnostics could mean better treatments and lower rates of disability and suicide. Some have even suggested more thorough, proficient screening might help to prevent the many tragic school shootings and spree killings that have shaken the US.
Researchers at Rockefeller University, Weill Cornell University and Stanford University may have taken an important step in that direction.
When they tested the blood of their 71 patients, they found that those who had previously been diagnosed with major depressive disorder had notably lower levels of a molecule called acetyl-L-carnitine (LAC).
This single compound plays a role in a number of key brain and body processes. It helps to coordinate our metabolism and acts as a conductor, turning genes on and off.
Perhaps the most important genetic switch that LAC flicks on and off codes for our glutamate levels. This neurotransmitter ‘excites’ neurons, revving them up for activation.
But too much glutamate can lead to a state of potentially deadly over-excitement for these brain cells, called ‘excitotoxicity.’ The brain has more glutamate than any other neurotransmitter, so it is crucial that there is also enough LAC to keep it in check and tell the transmitter when to give neurons a rest.
‘In patients with depression, something is causing a problem in the mechanisms related to the biology of LAC,’ said study co-author Dr Carla Nasca of Rockefeller University and the American Foundation for Suicide Prevention.
‘And, surprisingly, the deficiency in LAC is even stronger in patients that don’t respond to standard antidepressants.’
Her lab’s previous research on animals showed LAC supplements may even reduce depressive symptoms.
So the biomarker of depression scientists, physicians and patients have long hoped to find may even offer a new treatment pathway.
The lowest levels of LAC were found in those with a history of trauma or PTSD, in women and those with difficult-to-treat depression, signalling that there may be a very close relationship between these important stressors and this single molecule.
‘These findings should motivate research into the action of LAC on glutamate function and behavioral states,’ said study co-author Dr Bruce McEwen.
‘Additional research into other novel biomarkers to more precisely pinpoint major depressive disorder (MDD) diagnosis could ultimately lead to a different way of thinking about treatments for MDD and other disorders,’ he said.